1. Field of Invention
The current invention relates generally to apparatus, systems and methods for synthetic instruments. More particularly, the apparatus systems and methods relate to clocks for synthetic instruments. Specifically, the apparatus, systems and methods relate to amplifying and filtering clocks for use in synthetic instruments.
2. Description of Related Art
Synthetic Instrument (SI) units are modern measurement and stimulus systems. Unlike traditional instrumentation systems, the SI user may not be constrained by legacy frequency plans. Traditional downconverter frequency plans were born from technology available in the 1960s and 1970s. High frequency gain was either not available or was very expensive. Therefore, the bulk of the system's gain was obtained at a relatively low Intermediate Frequency (IF) and was usually passed along to the Analog-to-Digital Converter (ADC). Typical IF choices were 455 KHz, 10.7 MHz or 21.4 MHz, for example, which led to large filter components in order to meet rejection requirements. Low loss, sharp transition filters required large, low loss elements. In the past, these constraints were not a problem because other system components were of comparable size. Narrow filters were the norm because data bandwidth requirements were minimal.
As RF technology has improved, it is now possible to obtain more of the system gain at higher frequencies. Broadband, flat frequency response components are now available. The rapid technological advancement in the cellular telephone industry generated thousands of new, low cost microwave amplifiers, filters, and switches. At the same time, the speed and quality of ADCs has improved. From a round 1995 to 2003 ADCs used for low band operation improved from 12-bits at 41MSPS to 12-bits at 400MSPS. In 2009, the benchmark was 16-bits at 200MSPS. That is a 20:1 improvement in 14 years.
Present signal bandwidth requirements are much wider because the type of data transmission has changed. To make a practical architecture, it is necessary to limit the bandwidth percentage for a given IF frequency because it avoids the risks of filter induced, phase distortion and makes physical realization possible. The same filter design that obtains sharp attenuation properties does so at the expense of large phase changes over the filter's passband. A SI must support legacy analog as well as high speed digital signals. Therefore, frequency and time domain characteristics can both be important.
This goal is difficult to meet when using an IF and frequency plan with an IF designed to pass narrow bandwidth signals. An SI-based system is not compartmentalized into the stand alone architecture of legacy measurement hardware. The SI concept is to share functional blocks to perform multiple tasks with a limited number of blocks. The newer components of a modern synthetic instrument system provide for designing the RF channel based on the signal requirements of SI. Thus, there is a need for an improved synthetic instrumentation system.